n. A member of the Ostracoda, an order of tiny marine and freshwater crustaceans with a shrimplike body enclosed in a bivalve shell.
Syn. -- seed shrimp, mussel shrimp. [ WordNet 1.5 ]

‖prop. n. pl. (Zool.) An order of Entomostraca possessing shrimplike bodies enclosed in hard bivalve shells; called also seed shrimp and mussel shrimp. They were formerly referred to as Ostracoidea. They are of small size, and swim freely about; many are less than 1 mm in length. Microfossils of certain extinct orders have been found extending back to the Cambrian age. [ 1913 Webster +PJC ]

n. Same as ostracod. [ PJC ]

n. Any of several extinct fishlike jawless vertebrates having a heavily armored body; of the Paleozoic. [ WordNet 1.5 ]

‖prop. n. pl. [ NL., fr. Gr. 'o`strakon shell of a testacean + &unr_; skin. ] (Zool.) A suborder of fishes of which Ostracion is the type. [ 1913 Webster ]